[FFmpeg-user] How to select x264 preset when do ffmpeg 2-pass encoding is helpful for quality ?

[littlebat]

On Mon, 7 Oct 2013 09:43:27 -0800
Lou <lou at lrcd.com> wrote:

> On Mon, 7 Oct 2013 19:04:36 +0800
> littlebat <dashing.meng at gmail.com> wrote:
> 
> > A question: If a slower preset is helpful for the quality at a
> > specified bitrate when do a 2-pass encoding with libx264 encoder?
> 
> Sorry, but I don't quite understand the question.

For example, a given video bitrate is 1024kbps, when do only one-pass
encoding, we select a slower preset will gain a better quality. But,
when I do the 2-pass encoding, if I select a slower preset in both the
first and second pass, if will I can still gain a better quality than
we use a faster preset in both the first and second pass? Or, the preset
is no influence on the quality in a 2-pass encoding?

I read the FFMpeg wiki page:
https://ffmpeg.org/trac/ffmpeg/wiki/x264EncodingGuide#twopass
It seems don't clarify this question.


> > For example: select "ultrafast" in pass 1 and "veryslow" in pass 2,
> > or, select "ultrafast" for both 2 passes?
> 
> You should use the same preset for both passes to avoid errors such
> as: [libx264 @ 0x20ac580] different weightp setting than first pass
> (1 vs 2)
> 
> Note that the first pass should have "turbo" settings applied (disable
> slower options generally not useful for first pass) unless x264 option
> --slow-firstpass is used (maybe there are some exceptions).